Amplifying ultrasonic waveguides

ABSTRACT

Ultrasonic waveguides having improved velocity gain are disclosed for use in ultrasonic medical devices. Specifically, the ultrasonic waveguides comprises a first material having a higher acoustic impedance and a second material having a lower acoustic impedance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 11/301,118, filed on Dec. 12, 2005, which is incorporated inits entirety by reference.

BACKGROUND OF DISCLOSURE

The present disclosure generally relates to improved ultrasonicwaveguides. More particularly, the present disclosure relates toultrasonic waveguides having improved amplification and reduced modalcoupling suitable for use in ultrasonic medical devices such asultrasonic scalpels, phacoemulsifiers, soft tissue aspirators, otherultrasonic surgical tools, and the like.

Many modern surgical procedures involve the use of ultrasonic surgicaldevices that typically operate at frequencies between 20 kHz and 60 kHz.These devices have application in many surgical specialties including,for example, neurosurgery, general surgery, and ophthalmic surgery. Ingeneral, it is known that ultrasonic surgical devices generateultrasonic frequency vibratory energy that is applied to an ultrasonicapplicator that vibrates longitudinally and which contacts the tissuesof a patient. The ultrasonic surgical device may, among other surgicaleffects, cut, fragment, and/or coagulate the contacted tissues of thepatient.

Ultrasonic surgical devices are constrained in their ability to generateultrasonic frequency vibratory energy due to limits inherent in thephysical characteristics of the materials typically used to fabricatethe devices. For example, titanium alloys are often used for fabricationof the ultrasonic waveguide that is used to contact the tissues of apatient (i.e., ultrasonic applicator). Titanium alloys have inherentfatigue strength and stress limitations that cannot be exceeded or theultrasonic applicator will crack and/or break resulting in an unusabletool. As a further example, an ultrasonic waveguide, such as for use asan ultrasonic transducer to convert supplied electrical power toultrasonic frequency vibratory energy, may be fabricated in astepped-down fashion; that is, geometrically stepping down the diameterof the transducer. While the smaller diameter end of the transducer willtypically have a higher amplitude and thus higher tip velocity due tothe stepping down, the stepping down leads to considerable stresses atthe step, which can result in less efficient transmission of energy,overheating of the transducer, and increased risk of failure.

Additionally, a phenomenon referred to as “modal coupling” can also beresponsible for establishing the upper performance boundary of anultrasonic surgical device. Modal coupling occurs when the vibratoryamplitude of an ultrasonic waveguide of an ultrasonic surgical device isincreased to such a level that the ultrasonic frequency vibratory energyat the desired resonant frequency is coupled to other modes ofvibration, commonly referred to as “parasitic modes”. The parasiticmodes of vibration may be at lower frequencies, near-by frequencies, orhigher frequencies, depending on the design of the system. The parasiticmodes of vibration may be longitudinal modes or they may be transversemodes, or they may be more complicated coupled modes. Modal coupling isespecially troublesome when the ultrasonic waveguide is an elongateprobe or catheter with a length greater than one wavelength at theresonant frequency of the particular ultrasonic surgical device;however, modal coupling may also occur for ultrasonic waveguides shorterthan one wavelength and for ultrasonic waveguides that are not shapedlike an elongate probe, for example, flat or convex radiating surfaces.

The most common type of modal coupling encountered for ultrasonicsurgical devices is the stimulation of a lower or near-by frequencytransverse mode so that the ultrasonic waveguide vibrates in the desiredlongitudinal vibratory mode and an undesired transverse vibratory modesimultaneously. This type of coupled vibration can easily cause stressesin the ultrasonic waveguide material sufficient to break the ultrasonicwaveguide.

Ultrasonic surgical devices that operate at high vibratory amplitudesmay also generate undesirable heat, primarily in the ultrasonictransducer, but also in the material of other ultrasonic waveguides suchas in an ultrasonic applicator, due to internal friction and otherlosses as the ultrasonic applicator vibrates. If the ultrasonictransducer becomes too hot during a typical procedure, active cooling,such as forced air or water cooling, of the ultrasonic transducer isrequired, making the ultrasonic surgical handpiece more expensive andmore cumbersome due to the additional supply lines. Also, if theultrasonic applicator becomes too hot, unwanted hot spots or unwantedactive zones can result, damaging the tissues of a patient.

Based on the foregoing, there is a need in the art for ultrasonicmedical devices and ultrasonic waveguides to be used in ultrasonicmedical devices that have good amplification but greatly reducedstresses and heat generation. It would also be desirable for theultrasonic waveguides to have a reduced risk of modal coupling.

SUMMARY OF THE DISCLOSURE

The present disclosure is directed to novel ultrasonic waveguides thathave improved amplification, yet have greatly reduced stresses and heatgeneration. Additionally, the ultrasonic waveguides have a reduced riskof modal coupling. Generally, the ultrasonic waveguides comprise acomponent body having a uniform cross-section formed by the process ofhot isostatic pressing (HIP) two or more materials. In one embodiment,the improved ultrasonic waveguide comprises a hot isostatically pressedcomponent body. The hot isostatically pressed component body comprises afirst material having a higher acoustic impedance and a second materialhaving a lower acoustic impedance. The improved waveguides can be usedin ultrasonic medical devices such as ultrasonic scalpels,phacoemulsifiers, soft tissue aspirators, and the like. Additionally,the improved waveguides can be used in other known ultrasonic tools.

As such, the present disclosure is directed to an ultrasonic waveguidecomprising a hot isostatically pressed component body. The hotisostatically pressed component body comprises a first material and asecond material. The first material has a higher acoustic impedance ascompared to the second material.

The present disclosure is further directed to an ultrasonic medicaldevice comprising a one-half wave resonant transducer coupled to aone-half wave ultrasonic waveguide. The one-half wave ultrasonicwaveguide comprises a hot isostatically pressed component bodycomprising a one-quarter wave first material and a one-quarter wavesecond material. The first material has a higher acoustic impedance ascompared to the second material.

The present disclosure is further directed to an ultrasonic waveguide,the ultrasonic waveguide comprising a hot isostatically pressedcomponent body. The hot isostatically pressed component body comprises afirst material and a second material. The first material has an acousticimpedance of 40×10⁵ (gm/cm² sec) or more. The second material has anacoustic impedance of less than 40×10⁵ (gm/cm² sec).

The present disclosure is further directed to an ultrasonic medicaldevice comprising a one-half wave resonant transducer coupled to aone-half wave ultrasonic waveguide. The one-half wave ultrasonicwaveguide comprises a hot isostatically pressed component bodycomprising a one-quarter wave first material and a one-quarter wavesecond material. The first material has an acoustic impedance of 40×10⁵(gm/cm² sec) or more and the second material has an acoustic impedanceof less than 40×10⁵ (gm/cm² sec).

Other features of the present disclosure will be in part apparent and inpart pointed out hereinafter.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic representation of a one-half wave ultrasonicwaveguide.

FIG. 2 is a schematic representation of a one-half wave ultrasonicwaveguide coupled to a one-half wave resonant transducer.

FIG. 3 is a schematic representation of a one-half wave resonanttransducer.

FIGS. 4A-C are graphs depicting the displacement at the diffusion bondof the ultrasonic assembly of the present invention as compared to thedisplacement at the step of a conventional stepped horn and thedisplacement at the diffusion bond of a conventional waveguide coupledto a transducer.

FIGS. 5A-C are graphs depicting the internal stress of the ultrasonicassembly of the present invention as compared to the internal stressesof a conventional stepped horn and a conventional waveguide coupled to atransducer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present disclosure is generally directed to ultrasonic waveguideshaving improved amplification and being suitable for use in ultrasonicmedical devices. During use, the ultrasonic waveguides of the presentdisclosure undergo less stress and reduced heat generation thanconventional ultrasonic waveguides. Additionally, the phenomenon ofmodal coupling is less likely to result with the ultrasonic waveguidesof the present disclosure, even at increased vibratory amplitudes. Assuch, when the ultrasonic waveguides as described herein are used inultrasonic medical devices, the devices are more energy efficient andhave a reduced risk of damaging the tissues of the patient.

Ultrasonic waveguides can be used as one or more of the components in anultrasonic medical device, or other ultrasonic tool. Typically, theultrasonic waveguides can either provide velocity gain from theultrasonic transducer to the operative work site (i.e., ultrasonicapplicator) or, alternatively, they can be used to transmit ultrasonicenergy to remote sites by a series of coupled one-half wave unity gainresonant sections. For example, in one embodiment, the ultrasonicwaveguide is a one-half wave ultrasonic waveguide coupled to anultrasonic resonant transducer to provide velocity gain from thetransducer to the work site. In another embodiment, a series of one-halfwave ultrasonic waveguides are coupled to each other to transmitultrasonic energy, such as that used in an ultrasonic scalpel forendoscopic surgical procedures.

An exemplary ultrasonic assembly 10 including an ultrasonic waveguide 12coupled to an ultrasonic resonant transducer 14 as described in thedisclosure is illustrated schematically in FIG. 1. That is, FIG. 1illustrates a one-half wave ultrasonic waveguide 12 having a hotisostatically pressed component body with a uniform cross-section area.As depicted in FIG. 1, the hot isostatically pressed component body ofthis embodiment comprises a proximal one-quarter wave section made of afirst material having a high acoustic impedance value 20 and a distalone-quarter wave section made of a second material having a loweracoustic impedance value 24.

Variables such as the diameter, mass, width, thickness, andconfiguration of the ultrasonic waveguide are not narrowly critical andwill depend on the type of ultrasonic medical device or other ultrasoniccomponent in which the ultrasonic waveguide is to be used. The physicalvariables do determine the particular frequency and amplitude at whichthe ultrasonic waveguide resonates and vibrates. In particular, thephysical variables of an acoustic device, e.g., an ultrasonic waveguide,such as diameter, mass, thickness, overall configuration etc. may beselected such that the waveguide resonates in a desired mode, i.e., afundamental resonant mode under a given set of conditions, at aparticular frequency and with a desired amplitude. For example, it isknown that vibration in the desired mode at a desired frequency isachieved by adjusting physical parameters, and it is known that velocitygain, calculated as the ratio of output amplitude to input amplitude,can be adjusted by adjusting physical parameters.

As noted above, the ultrasonic waveguides of the present disclosure haveimproved amplification, which further produces an improved velocitygain, by employing a first material having a higher acoustic impedanceand a second material having a lower acoustic impedance to form the hotisostatically pressed component body. In one specific embodiment, thefirst material is a metal and the second material is a metal differentthan the first metal.

The first material has a high acoustic impedance. In one embodiment, thefirst material has an acoustic impedance of 40×10⁵ (gm/cm² sec) or more.More suitably, the first material of this embodiment has an acousticimpedance of greater than about 100×10⁵ (gm/cm² sec).

The first material for use in the hot isostatically pressed componentbody is suitably selected from the group consisting of copper, gold,iron, molybdenum, MONEL™ (nickel-copper alloy), nickel, platinum, steel,stainless steel, tungsten, and uranium. One particularly preferred firstmaterial is tungsten.

The second material for use in the hot isostatically pressed componentbody suitably has a lower acoustic impedance as compared to the firstmaterial. For example, in one embodiment, the second material has anacoustic impedance of less than 40×10⁵ (gm/cm² sec). Suitable materialsfor use as the second material include, for example, aluminum,beryllium, brass, cadmium, lead, magnesium, mercury, silver, tin,titanium, and zinc. One particularly preferred second material isaluminum.

As noted above, the ultrasonic waveguides of the present disclosure haveimproved amplification as compared to conventional ultrasonicwaveguides. Generally, ultrasonic amplification can be determined usingthe theory and equations described in Julian Frederick's “UltrasonicEngineering”, Wiley, 1965. Specifically, the ultrasonic amplification ofmotion that can be obtained by using two different materials in anultrasonic waveguide is given by either of the following equations:M=(ρ₁ c ₁)/(ρ₂ c ₂)orM=√(E ₁ρ₁ /E ₂ρ₂)

wherein ρ₁, c₁, and E₁ are density, sound velocity (bar) and Young'smodulus of one material, and ρ₂, c₂, and E₂ are the correspondingquantities for the other material. The subscripts are assigned to ρc andEρ so that ρ₁c₁>ρ₂c₂ or E₁ρ₁>E₂ρ₂. As such, it is apparent thatdifferences in both the density and Young's modulus, can be utilized toobtain an increase in the displacement or the velocity of one end of anultrasonic waveguide with respect to the other end.

Since an ultrasonic waveguide that is constructed using two differentmaterials will vibrate with a larger amplitude at the less dense endthan it would if both ends were of the same material, amplification canbe increased by using a more dense first material and a less densesecond material. With this configuration, the ultrasonic waveguide willtypically have a higher amplitude and, thus, a higher velocity gain atthe end contacting the tissue of the patient.

As noted above, the improved amplification of the ultrasonic waveguidesleads to improved velocity gain, which is measured as the ratio ofoutput amplitude to input amplitude. Suitably, the ultrasonic waveguidesof the present disclosure are capable of producing a velocity gain offrom about 1.5 to about 6.0. More suitably, the ultrasonic waveguidesare capable of producing a velocity gain of from about 1.8 to about 5.9,and even more suitably, from about 1.8 to about 4.0.

The ultrasonic waveguides of the present disclosure suitably include ahot isostatically pressed component body characterized by a uniformcross-section area. As a result of this structure, the ultrasonicwaveguides have less internal stress as compared to conventionalstepped-down-type ultrasonic waveguides. The internal stress of anultrasonic waveguide can be determined using a commercially availablecomputer modeling program such as Piezo Trans® software (available fromPiezoInnovations). Specifically, there is less internal stress at thediffusion bonded joint between the first material and the secondmaterial of the ultrasonic waveguides as compared to the internal stressat the step of conventional step waveguides or horns.

Suitably, the ultrasonic waveguides of the present disclosure have aninternal stress of less than about 1500 megapascals (Mpa). Moresuitably, the ultrasonic waveguides of the present disclosure have aninternal stress of less than about 1000 Mpa, and even more suitably,less than about 500 Mpa. Preferably, the ultrasonic waveguides of thepresent disclosure have an internal stress of from about 150 Mpa toabout 400 Mpa.

In addition to a uniform cross-section, due to being hot isostaticpressed as described more fully below, the hot isostatically pressedcomponent body of the ultrasonic waveguide has a microstructurecharacterized by random directional grain alignment and is isotropic inthat there is no preferential alignment in any direction or directions,such that the hot isostatically pressed component body uniformly expandsand contracts in all radial directions upon excitation at a frequencybetween about 20 kHz and about 60 kHz. The fact that there is nopreferential alignment of grains in any one direction, and that thedirectional alignment of grains is substantially isotropic and random,yields a hot isostatically pressed component body and, ultimately, anultrasonic waveguide which expands relatively uniformly in all radialdirections, in contrast to forged components which expand relativelynon-uniformly in various directions. This more relatively uniformexpansion characteristic results in increased uniformity in the workbeing performed. Specifically, the increased uniformity may preventunwanted hot spots or unwanted active zones, which can result indamaging the tissues of a patient.

The hot isostatically pressed component body of the present disclosurein certain physical embodiments where mechanical-type work is performedcan also be characterized by reduced maintenance requirements in thatthe uniformity of expansion and contraction can reduce the incidence ofwear and deformation on the working surface, because there are not areasof substantially differing impact force.

A further advantage of the waveguides as described herein is that theneed for tuning the hot isostatically pressed component body can beeliminated or substantially reduced. In particular, it has beendiscovered that a HIP-consolidated microstructure has a more consistentresonant operating frequency from component to component than does aforged microstructure. As such, a HIP-consolidated ultrasonic waveguideor other component of a specific predetermined configuration diameterwill much more consistently and predictably have a resonant operatingfrequency of, for example, 20,000 Hz. Accordingly, a 20,000 Hz waveguideor other component can more reliably be produced by simply machiningdirectly to this predetermined configuration, without the need toproduce it oversize and gradually machine it to reduce its diameteruntil the proper frequency is achieved. This is believed to be due tothe fact that the HIP-consolidated material has a grain sizedistribution and grain alignment which does not vary substantially fromone component to the next, as does the grain size distribution and grainalignment of forgings.

It has been discovered that HIP-consolidation is especially suited formanufacture of the components of the disclosure because it yields theisotropic microstructure of conventional powder metal sintering, withouta sacrifice in density which accompanies sintering; and that it achievesthe density of forging, without the non-isotropic microstructure offorging.

A further advantage of the waveguides of the present disclosure is theavoidance of undesired coupling of operating modes which is sometimespresent with forged components. In particular, the directional alignmentof grains in a forged component results in coupling or linkage of morethan one mode of potential expansion and contraction upon excitation.Under certain operating conditions more than one of these modes can bemanifested, resulting in non-uniform expansion and contraction. In someinstances where a large number of modes are coupled, the component maynot even operate, rendering it scrap. Components forged from a highlydirectional billet, for example, may have as high as a 30% scrap rate.In contrast, the hot isostatically pressed component body of theultrasonic waveguide of the disclosure operates in only one mode, thatbeing the mode for which it is designed according to acoustical designprinciples, due to its microstructure being isotropic, such thatundesired coupling of more than one operational mode is avoided.

A still further advantage of the waveguides of the present disclosure isthat each successive hot isostatically pressed component body hasessentially the same microstructure. As such, each one will haveessentially the same operational mode, thus lending predictability tothe manufacturing process. In contrast, forgings do not have asconsistent microstructure from one forging to the next, such that theoperation modes, or primary expansion and contraction characteristics,vary from one forging to the next.

As noted above, the ultrasonic waveguides can be used in ultrasonicmedical devices. Suitable examples of ultrasonic medical devicescomprising the ultrasonic waveguides of the present disclosure caninclude ultrasonic scalpels, phacoemulsifiers, soft tissue aspirators,other ultrasonic surgical tools, and the like.

Ultrasonic medical devices, such as ultrasonic scalpels, typicallycomprise multiple ultrasonic waveguides used in series. In one preferredembodiment, the ultrasonic medical device includes a one-half waveresonant transducer coupled with a one-half wave ultrasonic waveguide.The one-half wave ultrasonic waveguide comprises a hot isostaticallypressed component body, as described above, comprising a one-quarterwave first material and a one-quarter wave second material. Materialsfor use as the first material and the second material are describedabove.

When the ultrasonic medical device includes coupling an ultrasonicwaveguide as described herein to another ultrasonic component, such as aresonant transducer, the ultrasonic waveguide can be coupled with theother component using any means known in the art. For example, in oneembodiment, the ultrasonic waveguide can be coupled to the transducer bya connector, such as a solid pin or threaded stud. In anotherembodiment, the ultrasonic waveguide can be coupled to the transducer bya metallurgical fusion zone produced by metallurgically fusing thecomponents together. As discussed more fully below, in one embodiment,the fusion zone can be produced by hot isostatic pressing.

As with the ultrasonic waveguide described above, the ultrasonic medicaldevice including the ultrasonic waveguide of the present disclosure hasboth an improved amplification and velocity gain and a reduced internalstress as determined using the methods described above. Specifically,the ultrasonic medical device produces a velocity gain of from about 1.5to about 6.0, more suitably, a velocity gain of from about 1.8 to about5.9, and even more suitably, from about 1.8 to about 4.0. Additionally,the ultrasonic medical devices have an internal stress of less thanabout 1500 Mpa. More suitably, the ultrasonic medical devices of thepresent disclosure have an internal stress of less than about 1000 Mpa,and even more suitably, less than about 500 Mpa. Preferably, theultrasonic medical device has an internal stress of from about 150 Mpato about 400 Mpa.

Additionally, the present disclosure is directed to methods ofmanufacturing the ultrasonic waveguides and ultrasonic medical devicesdescribed herein above. For example, in one embodiment, the method formanufacturing an ultrasonic waveguide of the present disclosure includesthe following steps: (1) filling an ultrasonic waveguide preform with afirst material having an acoustic impedance of 40×10⁵ (gm/cm² sec) ormore and a second material having an acoustic impedance of less than40×10⁵ (gm/cm² sec); and (2) hot isostatic pressing the ultrasonicwaveguide preform to consolidate the first material and the secondmaterial to form a hot isostatically pressed component body.

As noted above, the first step in the method for manufacturing anultrasonic waveguide includes filling an ultrasonic waveguide preformwith a first material and a second material. The first material and thesecond material can be used in powder form, slug form, solid form, orcombinations thereof to produce the ultrasonic waveguide preform. Thefirst and second materials can be added into the preform by any methodknown in the art. In one embodiment, the ultrasonic waveguide preform isfilled with the first material and the second material, each in slugform.

In one embodiment, when filling the ultrasonic waveguide preform withthe first and second materials, the first material is added and then thesecond material is added to the preform. In another embodiment, thesecond material is added and then the first material is added to thepreform.

Typically, the ultrasonic waveguide preform is manufactured larger thanneeded and is then machined down to the desired size. The ultrasonicwaveguide preform is machined down using any method known in the art.Suitably, the preform is machined down to a one-half wave lengthdimension.

After filling the ultrasonic waveguide preform with the first and secondmaterials, the preform is hot isostatic pressed to consolidate the firstmaterial and the second material to form a hot isostatically pressedcomponent body. The method of hot isostatic pressing is well known inthe art of ultrasonic horns, such as horns used for bonding twothermoplastic sheets of materials together in the manufacture ofpersonal care products such as diapers. As noted above, the presentdisclosure uses the method of hot isostatic pressing to produce a hotisostatically pressed component body of an ultrasonic waveguide for usein ultrasonic medical devices.

One suitable method of producing the hot isostatically pressed componentbody includes employing a pressure vessel which can be pressurizedemploying a gas, such as argon, of commercial quality to apply apressure equally over the entire surface area of the hot isostaticallypressed component body. The pressure, in combination with the elevatedtemperature employed, effects consolidation of the materials to adensity of at least about 95%, at least about 99%, and even about 100%of the theoretical density of the materials. With this density, the hotisostatically pressed component body has a microstructure that issubstantially totally void free. As used herein, the term “substantiallyvoid free” refers to a microstructure being 95% free of voids or gaps.Suitably, a microstructure that is substantially void free is 98% freeof voids or gaps, more suitably, 99% free of voids, and even moresuitably, 100% free of voids.

As the hot isostatically pressed component body is substantially voidfree, the hot isostatically pressed component body is more resistant tocontamination by micro-organisms such as prions. This is especiallypreferable when working in the medical field such as with ultrasonicmedical devices.

For the hot isostatic pressing, a pressure suitable for use in thisoperation can be, for example, from about 14 ksi to about 16 ksi. Moresuitably, the pressure for use in hot isostatic pressing of the preformis about 16 ksi. The temperature employed in this operation can be inthe range of about 1400° F. (about 760° C.) to about 1600° F. (about870° C.). The duration of the hot isostatic pressing step depends uponthe temperature and pressure selected. As a general proposition, whenthe pressure is 16 ksi and the temperature is in the range of about1400° F. (about 760° C.) to about 1600° F. (about 870° C.), the processmay employ a time period of about 1.5 hours to about 3 hours, forexample 2 hours, in one embodiment. At the conclusion of the hotisostatic pressing step, the component body is held in the hot isostaticpressing pressure vessel and allowed to cool to ambient temperature(about 23.7° C.) and is then removed from the pressure vessel.

The hot isostatically pressed component body is then optionallysubjected to final machining operations to impart the desired shape andsurface characteristics of the ultrasonic waveguide as described above.

Once the ultrasonic waveguide is manufactured, the ultrasonic waveguidecan be utilized to manufacture an ultrasonic medical device. Forexample, in one embodiment, the present disclosure is directed to amethod of manufacturing an ultrasonic medical device by coupling theone-half wave ultrasonic waveguide as manufactured above to a one-halfwave resonant transducer.

A suitable resonant transducer may be produced by any means in the art.Alternatively, the resonant transducer may be obtained commercially fromZevex, Inc. (Salt Lake City, Utah).

In one embodiment, the resonant transducer is a composite transducer,constructed as shown in FIG. 3, which comprises a first material 40, asecond material 42 and a piezoelectric crystal 46. Materials for use asthe first and second materials of the composite transducer are the sameas those described above for use in an ultrasonic waveguide. In oneembodiment, the transducer may be further mounted in a fixture or in aprotective case by means of the nodal mounting plate 48.

As noted above, any method of coupling ultrasonic components can be usedto couple the one-half wave ultrasonic waveguide to the one-half waveresonant transducer. In one embodiment, the one-half wave ultrasonicwaveguide is coupled to the one-half wave resonant transducer using amechanical connector. Suitable connectors for use in coupling thecomponents can include, for example, solid pins, threaded studs, and anycombination thereof. One suitable embodiment comprises using a solid pinhaving a clearance of 0.001 inch or less to provide an interference fitbetween the components as the connector. In another preferredembodiment, the connector may be partially or fully threaded studspassing through the interfaces. The connectors of any type may be formedfrom the same materials as the components.

In another embodiment, the one-half wave ultrasonic waveguide is coupledto the one-half wave resonant transducer by metallurgical fusion, whichcreates a fusion zone on the interface of the ultrasonic waveguide andresonant transducer. As shown in FIG. 2, the interface 26 is thelocation of engagement of the energy transfer face of the ultrasonicwaveguide 32 to the energy transfer face of the resonant transducer 36.The transfer faces are lapped to be flattened to within two millionthsof an inch and thoroughly cleaned with acetone prior to assembly.

Suitably, the fusion zone created by metallurgical fusing the componentsfacilitates more efficient ultrasonic energy transfer between therespective components because it serves to integrate the components toeach other, thus eliminating loss of energy between the components atthe transfer interface. Moreover, the fusion zone eliminates the needfor periodic disassembly to remove wear and oxide on the respectivetransfer faces of the waveguide and transducer.

In one preferred embodiment, hot isostatic pressing forms these fusionzones. The ultrasonic waveguide and resonant transducer are subjected tohot isostatic pressing in a single pressing operation for the entireassembly. Typically during the hot isostatic pressing step, ahigh-strength uniform metallurgical diffusion bond is formed between thetransfer faces. The resultant metallic fusion formed is characterized asnot appreciably indicating a line of demarcation between the components,but rather a uniform transformation of grain structure characteristic ofan integral assembly. In one embodiment, the fusion zone can extend fromon the order of 0.001 inch (0.0025 cm) into each component to on theorder of several thousandths of an inch, such as 0.005 inch (0.0075 cm)into each component, for a total fusion zone width of between about0.002 inch (0.005 cm) and about 0.01 inch (0.025 cm). In otherembodiments, the fusion zone may be wider or narrower.

To prepare the coupled components for the fusion procedure such as hotisostatic pressing, it is first suitable, but not required, to subjectseams at the interfaces to a preliminary sealing operation to bring thetransfer faces into more intimate contact and to seal the interfacesfrom external air or atmosphere during hot isostatic pressing. In oneembodiment, this is accomplished by electron beam welding as is wellunderstood in the metals joining art, involving a vacuum process toremove any residual air from between the components at their interface,followed by electron beam welding to seal the hairline interface alongthe exposed outside of the interfaces. By sealing this interface undervacuum conditions, all air or atmosphere is prevented from interferingwith subsequent fusion by hot isostatic pressing.

One suitable method of hot isostatic pressing of the components can becarried out similar to the hot isostatic pressing of the first materialand second material of the ultrasonic waveguide as described above.Specifically, the components can be hot isostatic pressed by employing apressure vessel which can be pressurized employing gas, such as argon,of commercial quality to apply a pressure equally over the entiresurface area of the assembly. The pressure, in combination with theelevated temperature employed, affects a 100% fusion bonding across theinterfaces causing them to become totally integrated to an interfacedensity approaching 100% theoretical density. A pressure suitable foruse in this operation range can be, for example, about 16 ksi. Thetemperature employed in this operation can be in the range of about1500° F. (815° C.) to about 1600° F. (870° C.) The duration of the hotisostatic pressing step depends upon the temperature and pressureselected. As a general proposition, when the pressure is 16 ksi and thetemperature is in the range of about 1500° F. (815° C.) to about 1600°F. (870° C.), the process may employ a time period of from about 1.5hours to about 3 hours, for example 2 hours, in one embodiment. At theconclusion of the hot isostatic pressing step, the assembly is cooledand removed from the pressure vessel.

EXAMPLE

The following example is simply intended to further illustrate andexplain the present disclosure.

The disclosure, therefore, should not be limited to any of the detailsin this example.

Example 1

In this Example, a one-half wave ultrasonic waveguide comprising a hotisostatically pressed component body comprising one-quarter wavetungsten and one-quarter wave aluminum was produced. This one-half waveultrasonic waveguide was then coupled to a commercially availableresonant transducer (available from Zevex, Inc. (Salt Lake City, Utah))to produce an ultrasonic assembly. The velocity gain and internal stressof this ultrasonic assembly was then evaluated and compared to thevelocity gain and internal stress of a one wave conventional steppedhorn assembly made from a one-half wave ultrasonic waveguide of tungstenand a conventional resonant transducer and the velocity gain andinternal stress of a one-half wave tungsten waveguide/one-half waveresonant transducer assembly. The conventional stepped horn assembly wasmade using tungsten in a conventional stepped horn process to form theone-half waveguide of tungsten and connecting the one-half waveguide oftungsten with a resonant transducer (available from Zevex, Inc. (SaltLake City, Utah)) using a threaded stud. The one-half wave tungstenwaveguide/one-half wave resonant transducer assembly was made by fillingan ultrasonic waveguide preform with tungsten and then subjecting thepreform to a conventional hot isostactic pressing process. The one-halfwave tungsten waveguide was then connected to the commercially availableresonant transducer (available from Zevex, Inc. (Salt Lake City, Utah))using a threaded stud.

To produce the one-half wave ultrasonic waveguide comprising a hotisostatically pressed component body, a tungsten slug (such as availablefrom Alfa Aesar, Ward Hill, Mass.) having an acoustic impedance of101.0×10⁵ (gm/cm² sec) was introduced into an ultrasonic waveguidepreform (commercially available from Bodycote, Andover, Mass.) and thenan aluminum slug (such as available from JLO Metal Products, Inc.,Chicago, Ill.) having an acoustic impedance of 17.0×10⁵ (gm/cm² sec) wasintroduced into the ultrasonic waveguide preform. The ultrasonicwaveguide preform was then hot isostatic pressed using a conventionalhot isostatic pressing process to form a hot isostatically pressedcomponent body having about 100% density.

The tungsten-aluminum one-half wave ultrasonic waveguide was thenmachined to the desired size and coupled to a conventional one-half waveresonant transducer comprised of steel and aluminum using a threadedstud.

Physical characteristics, such as diameter and length of thetungsten-aluminum ultrasonic assembly, stepped tungsten horn assembly,and tungsten waveguide/transducer assembly were substantially the same.Additionally, the transducer of the assemblies were set to operate at afrequency of 40 kHz.

The amplification of the three assemblies were then determined at 40kHz. The amplification of the tungsten-aluminum ultrasonic assembly wasdetermined using the formula set forth above in the specification.Specifically, the amplification of the tungsten-aluminum ultrasonicassembly is equal to the product of the density and sound velocity oftungsten divided by the product of the density and sound velocity ofaluminum. The amplification of the stepped tungsten horn assembly wasdetermined using the formula:

${Amplification} = \frac{{larger}\mspace{14mu}{diameter}}{{smaller}\mspace{14mu}{diameter}}$

The amplification of the tungsten waveguide/transducer assembly wasdetermined using a Laser Vibrometer (commercially available from PolytecPI, Inc., Auburn, Mass.).

In addition to the amplification, the velocity gain during operation ofeach of the tungsten-aluminum ultrasonic assembly, stepped tungsten hornassembly, and tungsten waveguide/transducer assembly were thendetermined by measuring the displacement of output amplitude to inputamplitude at the diffusion bond joint or step between the one-quarterwave component nearest to the resonant transducer and the one-quarterwave component farthest from the resonant transducer. The velocity gainsof each of the assemblies were then compared. The results are shown inFIGS. 4A-C.

As shown in FIGS. 4A-4C, the displacement at the diffusion bond of thetungsten-aluminum ultrasonic assembly was substantially the same as thedisplacement at the step of the stepped tungsten horn assembly. As such,the tungsten-aluminum ultrasonic assembly had the same velocity gain asthe stepped tungsten horn assembly. The tungsten waveguide/transducerassembly, however, had a much lower velocity gain. Specifically, thedisplacement at the diffusion bond joint of the tungstenwaveguide/transducer assembly was approximately 17.5 microns, while thedisplacement at the diffusion bond joint of the ultrasonic assembly wasapproximately 100 microns.

The internal stresses at each of the diffusion bonded joints of thetungsten-aluminum ultrasonic assembly and of the tungstenwaveguide/transducer assembly and the internal stress at the step of thestepped tungsten horn assembly were then determined using Piezo Trans®software (available from PiezoInnovations). The results are shown inFIGS. 5A-C.

As shown in FIGS. 5A-C, the internal stress at the diffusion bondedjoint between the one-quarter wave tungsten and one-quarter wavealuminum of the tungsten-aluminum ultrasonic assembly was approximately360 MPa. The internal stress at the diffusion bonded joint between thetungsten waveguide and transducer of the tungsten waveguide/transducerassembly was also approximately 360 MPa. The internal stress on the stepof the stepped tungsten horn assembly, however, was approximately 2100MPa. As such, due to the hot isostatic pressing-consolidation of the twomaterials in a preform having a uniform cross-section, the internalstresses put on the tungsten-aluminum ultrasonic assembly was almost sixtimes less than the internal stress on the step of the stepped tungstenhorn assembly, even with the same velocity gain.

In summary, using two different materials, having different acousticimpedances, for the one-quarter wave components provides an ultrasonicassembly providing an improved velocity gain, such as can be produced bya conventional stepped horn assembly, but without the disadvantage ofputting high internal stress on the assembly at the step.

In view of the above, it will be seen that the several objects of thedisclosure are achieved and other advantageous results obtained.

When introducing elements of the present disclosure or the preferredembodiment(s) thereof, the articles “a”, “an”, “the” and “said” areintended to mean that there are one or more of the elements. The terms“comprising”, “including” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements.

As various changes could be made in the above without departing from thescope of the disclosure, it is intended that all matter contained in theabove description and shown in the accompanying drawings shall beinterpreted as illustrative and not in a limiting sense.

What is claimed is:
 1. An ultrasonic waveguide comprising a hotisostatically pressed component body comprising a first material and asecond material, the first material having an acoustic impedance of40×10⁵ (gm/cm² sec) or more, and the second material having an acousticimpedance of less than 40×10⁵ (gm/cm² sec), wherein the entire hotisostatically pressed component body has a substantially uniformcross-section.
 2. The ultrasonic waveguide as set forth in claim 1wherein the first material is a metal and the second material is ametal.
 3. The ultrasonic waveguide as set forth in claim 1 wherein thefirst material has an acoustic impedance of greater than about 100×10⁵(gm/cm² sec).
 4. The ultrasonic waveguide as set forth in claim 1wherein the first material is selected from the group consisting ofcopper, gold, iron, molybdenum, (nickel-copper alloy), nickel, platinum,steel, stainless steel, tungsten, and uranium.
 5. The ultrasonicwaveguide as set forth in claim 1 wherein the first material istungsten.
 6. The ultrasonic waveguide as set forth in claim 1 whereinthe second material has an acoustic impedance of less than 25×10⁵(gm/cm² sec).
 7. The ultrasonic waveguide as set forth in claim 1wherein the second material is selected from the group consisting ofaluminum, beryllium, brass, cadmium, lead, magnesium, mercury, silver,tin, titanium, and zinc.
 8. The ultrasonic waveguide as set forth inclaim 1 wherein the second material is aluminum.
 9. The ultrasonicwaveguide as set forth in claim 1 being capable of producing a velocitygain of from about 1.5 to about 6.0.
 10. The ultrasonic waveguide as setforth in claim 1 having an internal stress of less than about 1500 MPa.11. The ultrasonic waveguide as set forth in claim 1 wherein the hotisostatically pressed component body comprises a microstructurecharacterized by isotropically random directional grain alignment. 12.The ultrasonic waveguide as set forth in claim 1 wherein the firstmaterial is tungsten and the second material is aluminum.
 13. Anultrasonic medical device comprising a one-half wave resonant transducercoupled with a one-half wave ultrasonic waveguide, wherein the one-halfwave ultrasonic waveguide comprises a hot isostatically pressedcomponent body comprising a one-quarter wave first material and aone-quarter wave second material, the first material having an acousticimpedance of 40×10⁵ (gm/cm² sec) or more, and the second material havingan acoustic impedance of less than 40×10⁵ (gm/cm² sec), wherein theentire hot isostatically pressed component body has a substantiallyuniform cross-section.
 14. The ultrasonic medical device as set forth inclaim 13 wherein the first material has an acoustic impedance of greaterthan about 100×10⁵ (gm/cm² sec).
 15. The ultrasonic medical device asset forth in claim 13 wherein the second material has an acousticimpedance of less than 25×10⁵ (gm/cm² sec).
 16. The ultrasonic medicaldevice as set forth in claim 13 wherein the first material is selectedfrom the group consisting of copper, gold, iron, molybdenum,(nickel-copper alloy), nickel, platinum, steel, stainless steel,tungsten, and uranium.
 17. The ultrasonic medical device as set forth inclaim 13 wherein the first material is tungsten.
 18. The ultrasonicmedical device as set forth in claim 13 wherein the second material isselected from the group consisting of aluminum, beryllium, brass,cadmium, lead, magnesium, mercury, silver, tin, titanium, and zinc. 19.The ultrasonic medical device as set forth in claim 13 wherein thesecond material is aluminum.